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UC2845A Datasheet Preview

UC2845A Datasheet

Current Mode PWM Controller

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Current Mode PWM Controller

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INFO

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UC1842A/3A/4A/5A

UC2842A/3A/4A/5A

UC3842A/3A/4A/5A

FEATURES

• Optimized for Off-line and DC to DC

Converters

• Low Start Up Current (<0.5mA)

• Trimmed Oscillator Discharge Current

• Automatic Feed Forward Compensation

• Pulse-by-Pulse Current Limiting

• Enhanced Load Response Characteristics

DESCRIPTION

The UC1842A/3A/4A/5A family of control ICs is a pin for pin compati-

ble improved version of the UC3842/3/4/5 family. Providing the nec-

essary features to control current mode switched mode power

supplies, this family has the following improved features. Start up cur-

rent is guaranteed to be less than 0.5mA. Oscillator discharge is

trimmed to 8.3mA. During under voltage lockout, the output stage

can sink at least 10mA at less than 1.2V for VCC over 5V.

The difference between members of this family are shown in the table

below.

• Under-Voltage Lockout With Hysteresis

• Double Pulse Suppression

• High Current Totem Pole Output

• Internally Trimmed Bandgap Reference

• 500kHz Operation

• Low RO Error Amp

Part #

UC1842A

UC1843A

UC1844A

UC1845A

UVLO On

16.0V

8.5V

16.0V

8.5V

UVLO Off

10.0V

7.9V

10.0V

7.9V

Maximum Duty

Cycle

<100%

<50%

BLOCK DIAGRAM

Note 1: A/B A = DIL-8 Pin Number. B = SO-14 Pin Number.

Note 2: Toggle flip flop used only in 1844A and 1845A.

SLUS224A - SEPTEMBER 1994 - REVISED APRIL 2002

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UC2845A Datasheet Preview

UC2845A Datasheet

Current Mode PWM Controller

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CONNECTION DIAGRAMS

ABSOLUTE MAXIMUM RATINGS (Note 1)

Supply Voltage (Low Impedance Source) . . . . . . . . . . . . . . 30V

Supply Voltage (ICC mA) . . . . . . . . . . . . . . . . . . . . Self Limiting

Output Current. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ±1A

Output Energy (Capacitive Load). . . . . . . . . . . . . . . . . . . . . 5µJ

Analog Inputs (Pins 2, 3). . . . . . . . . . . . . . . . . . . -0.3V to +6.3V

Error Amp Output Sink Current . . . . . . . . . . . . . . . . . . . . 10mA

Power Dissipation at TA ≤ 25°C (DIL-8) . . . . . . . . . . . . . . . . 1W

Storage Temperature Range . . . . . . . . . . . . . . -65°C to +150°C

Lead Temperature (Soldering, 10 Seconds) . . . . . . . . . . 300°C

Note 1. All voltages are with respect to Ground, Pin 5. Currents

are positive into, negative out of the specified terminal. Consult

Packaging Section of Databook for thermal limitations and con-

siderations of packages. Pin numbers refer to DIL package only.

SOIC-14 (TOP VIEW)

D Package

PLCC-20, LCC-20

(TOP VIEW)

Q, L Packages

UC1842A/3A/4A/5A

UC2842A/3A/4A/5A

UC3842A/3A/4A/5A

PACKAGE PIN FUNCTION

FUNCTION

N/C 1

Comp

N/C 3-4

VFB 5

N/C 6

ISENSE

N/C 8-9

RT/CT

N/C 11

Pwr Gnd

Gnd 13

N/C 14

Output

N/C 16

VC 17

VCC 18

N/C 19

VREF

SOIC-WIDE16 (TOP VIEW)

DW Package

N/C 1

N/C 2

COMP 3

VFB 4

ISENSE 5

RT/CT 6

N/C 7

N/C 8

DIL-8, SOIC-8 (TOP VIEW)

J or N, D8 Package

16 N/C

15 VREF

14 VCC

13 VCC

12 OUTPUT

11 GND

10 PWRGND

9 N/C

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UC2845A Datasheet

Current Mode PWM Controller

UC2845A Datasheet

Current Mode PWM Controller

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